1. Field of the Invention
The present invention relates to a disk cartridge containing a flexible recording disk, and more particularly, to techniques for stabilizing the flexible disk within the cartridge during high speed rotation and for centering the edge of the disk to facilitate head loading onto the disk.
2. Description of the Prior Art
Removable disk cartridges for storing digital electronic information typically comprise an outer casing or shell that houses a rotatable recording medium, or disk, upon which electronic information can be stored. The cartridge shell often comprises upper and lower halves that are joined together to house the disk. The disk is mounted on a hub that rotates freely within the cartridge. When the cartridge is inserted into a disk drive, a spindle motor in the drive engages with the disk hub in order to rotate the disk within the cartridge. The outer shell of the cartridge typically has some form of opening near its forward edge to provide the recording heads of the drive with access to the recording surfaces of the disk. A shutter or door mechanism is often provided to cover the opening when the cartridge is not in use to prevent dust or other contaminants from entering the cartridge and settling on the recording surface of the disk.
Many prior art disk cartridges and associated disk drive mechanisms, such as those disclosed in U.S. Pat. Nos. 4,503,474, 5,218,503 and 5,262,918, employ magnetic hard disk technology, i.e., the cartridges contain rigid magnetic media. An advantage of using a rigid magnetic disk is that the disk is relatively stable during high speed rotation in the disk drive. The magnetic heads of the drive "fly" closely over the recording surface to achieve increased storage densities with little or no wear on the recording surface. Removable hard disk cartridges typically have capacities in the hundreds of megabytes. However, hard disk media are relatively expensive thereby undesirably increasing the cost of these removable hard disk cartridges. The same drawbacks are generally true of optical disk cartridges as well.
Conventional floppy disk cartridges, such as the standard 3.5" floppy disk cartridge used in most personal computers, employ a flexible recording medium (i.e., floppy disk) and are generally cheaper to manufacture than the aforementioned hard disk cartridges. However, in a conventional floppy disk drive, the floppy disk is rotated at relatively low speeds (e.g., 300-720 rpm), and the magnetic heads of the drive apparatus contact the disk surface as it rotates in the drive. Because of the low rotation speeds, the performance of these floppy disk cartridges is greatly reduced. Additionally, a conventional floppy disk usually can store only a few megabytes of information. Moreover, because the magnetic heads of a conventional floppy disk drive contact the floppy disk surface, the heads wear on the disk as it rotates.
One type of prior art cartridge that employs flexible media but attains increased storage capacity and higher performance is referred to in the art as a "Bernoulli" cartridge. These cartridges employ "Bernoulli" surface or plate to stabilize the rotating flexible disk during high speed rotation. As the flexible disk is rotated at high speeds (e.g. 2400 rpm) over the Bernoulli plate, an air bearing is created between the flexible magnetic disk and the rigid Bernoulli surface such that a predictable spacing between the Bernoulli surface and the magnetic disk is established. Once the flexible magnetic disk is stabilized, a specially designed recording head can be brought into close proximity to the rotating disk to achieve increased recording densities and high performance. Unfortunately, however, two sided recording with opposing read/write heads on the same disk is extremely difficult. Furthermore, Bernoulli cartridges and drives require very tight manufacturing tolerances and are therefore relatively expensive to manufacture.
Recently, there have been attempts to employ hard disk type recording heads (e.g., Winchester heads) on flexible disk media. The combination of hard disk type recording heads and flexible recording media promises to provide relatively low cost storage capabilities. Such a combination is illustrated in FIGS. 1A and 1B. The flexible disk is rotated at relatively high speeds, e.g., 3600 rpm, and the hard disk type recording heads 42a, 42b are positioned on opposite sides of the flexible media. The heads 42a, 42b are disposed on respective suspension arms 40a, 40b that are springably biased toward each other. As the flexible media rotates, an air bearing is created between the heads and respective disk surfaces that opposes the tendency of the heads to move together. As a result, the heads "fly" closely over the surface of the flexible disk. Because the magnetic heads 42a, 42b are biased toward each other and would clamp together in the absence of the opposing forces created by the aerodynamics of the spinning media, they are sometimes referred to herein as "pinching-type" heads.
High speed magnetic recording using hard disk type heads on flexible disk media has been greatly limited, however, due to the dynamics of a rotating disk subjected to a spatially fixed load, such as that imposed by the recording heads of a disk drive. A spinning flexible disk will deflect in the axial direction under an external transverse load in such a fashion that a standing wave pattern is established in the media, i.e., the disk achieves resonance. FIGS. 2(a) and 2(b) are exaggerated illustrations of a rotating disk 14 in which standing wave patterns have been established due to an external transverse load, L. As illustrated in the Figures, the standing wave pattern is characterized by a series of "peaks" 8 and "valleys" 6. The number of peaks and valleys and their angular relationship to the load, define the "mode" of the standing wave. A more detailed discussion of the behavior of a rotating flexible disk under an external transverse load can be found in Benson, R. C. & Takahashi, T. T., Mechanics of Flexible Disks in Magnetic Recording, Adv. Info. Storage Syst., Vol 1., pp. 15-35 (ASME 1991) and in Benson, R. C. & Bogy, D. B., Deflection of a Very Flexible Spinning Disk Due to a Stationary Transverse Load, Transactions of the ASME, Vol. 45 (September 1978), both of which are incorporated herein by reference.
Depending on the mechanical properties of the flexible disk and the radial and vertical positions of the recording heads (i.e., load) with respect to the axis of the disk, the "mode" or pattern of the standing wave will vary. As the standing wave transitions from one mode to another, for example, from the mode illustrated in FIG. 2(a) to that illustrated in FIG. 2(b), the disk undergoes a phenomenon know as "disk snap". Under certain conditions, the disk will undergo violent vibration as it tries to switch back and forth between two different modes. Such violent vibration will adversely affect the head-disk interface making recording and/or retrieval of information unreliable and also creating a potential for damage to the recording heads or disk surface. Another manifestation of the "disk snap" problem is that a given disk may exhibit different modes in different drives, such that the magnetic read/write signal strength may vary. This greatly undermines the advantages of removability. The problem becomes even more acute as the speed of rotation of the disk is increased above 3600 rpm. Accordingly, if high speed recording on flexible disks using hard-disk type recording heads is to be successful, a mechanism is needed for stabilizing the media so that the standing wave pattern, or mode, does not change as the heads move radially of the disk.
Prior art techniques for stabilizing a flexible disk during high speed rotation are either impractical or simply do not address the standing wave problem. For example, while the aforementioned use of a Bernoulli plate will stabilize a flexible disk and reduce the amplitude of a standing wave, the close spacing between the disk and Bernoulli plate makes two sided recording extremely difficult. Moreover, very tight manufacturing tolerances must be observed in the production of Bernoulli cartridges, thereby increasing the cost of such cartridges.
Another prior art approach to disk stabilization is the stretched surface disk. In this approach, the outer rim of the disk is clamped and under tension. The stress can be adjusted to suppress any standing waves. However, the inertia of the rotating body is large, and like the Bernoulli cartridges, two sided recording on a single disk cannot be achieved.
U.S. Pat. No. 5,189,574 describes a technique that purports to stabilize a rotating flexible disk at speeds of about 3600 rpm. According to the disclosed technique, the disk is rotated between a pair of opposing "stationary plates" each separated from the surface of the disk by a distance of about 400-800 .mu.m. The '594 patent theorizes that the stationary plates serve to prevent the occurrence of turbulent air flow near the surface of the disk thereby reducing disk vibration and achieving stabilization. While some stabilization may be achieved, this technique fails to address the mode stabilization problem, since the elimination of turbulent flow near the surface of a disk cannot suppress the changes in standing wave patterns described above.
Accordingly, there is a need for a removable disk cartridge capable of stabilizing the standing wave pattern, or mode, of a flexible recording disk rotating at high speeds in order to prevent the occurrence of "disk snap" as the recording heads move between the outer and inner radii of the disk.
Another problem with the use of flexible media in a removable disk cartridge, particularly when the cartridge is used in conjunction with a disk drive that employs pinching-type magnetic recording heads, is that the vertical position of the edge of the disk proximate the head access opening in the disk cartridge may deviate from a nominal vertical position due to factors such as disk curl, vertical runout, hub tilt and air flow within the cartridge. Even when a rotating flexible disk has settled into a stable standing wave mode, the disk can still experience these changes in vertical position. Changes in the vertical position of the edge of the disk can interfere with the loading of pinching type heads onto the disk. The prior art has failed to address this additional problem. Accordingly, there is a further need for a flexible disk cartridge having means for vertically centering the edge of the rotating flexible disk within a predetermined tolerance in,order to facilitate head loading onto the media. Such a centering means should not interfere with the aerodynamics of the rotating disk.